Detection apparatus, power receiving apparatus, non-contact power transmission system and detection method

ABSTRACT

Disclosed herein is a detection apparatus including: a resonant circuit provided with a Q-factor measurement coil and one or more capacitors to serve as a circuit for receiving pulses; a response-waveform detecting section configured to detect the waveform of a response output by the resonant circuit in response to the pulses; and a Q-factor measuring section configured to measure a Q factor of the resonant circuit from the response waveform detected by the response-waveform detecting section. It is possible to increase the precision of detection of a metallic foreign substance existing between a power transmitting side and a power receiving side.

RELATED APPLICATION DATA

This application is a continuation of U.S. patent application Ser. No.15/271,852 filed Sep. 21, 2016, which is a continuation of U.S. patentapplication Ser. No. 13/689,100 filed Nov. 29, 2012, now U.S. Pat. No.9,482,702 issued Nov. 1, 2016, the entireties of which are incorporatedherein by reference to the extent permitted by law. The presentapplication claims the benefit of priority to Japanese PatentApplication No. JP 2011-280059 filed on Dec. 21, 2011 in the JapanPatent Office, the entirety of which is incorporated by reference hereinto the extent permitted by law.

BACKGROUND

The present disclosure relates to a detection apparatus for detectingexistence of a conductor such as a metal between a power transmittingapparatus and a power receiving apparatus. In addition, the presentdisclosure also relates to the power receiving apparatus, a non-contactpower transmission system and a detection method.

In recent years, a non-contact power transmission system for supplyingelectric power by adoption of a wireless technique is developedaggressively. Methods for supplying electric power by adoption of awireless technique include two methods to be described as follows.

One of the two methods is an electromagnetic induction method which isalready known widely. In the electromagnetic induction method, thedegree of junction between the power transmitting side and the powerreceiving side is very high so that electric power can be supplied fromthe power transmitting side to the power receiving side with a highdegree of efficiency. Since the coefficient of junction between thepower transmitting side and the power receiving side needs to be held ata high value, however, the efficiency of power transmission betweencoils on the power transmitting side and the power receiving sidedeteriorates considerably if the distance between the power transmittingside and the power receiving side increases or if the power transmittingside is shifted from a position exposed to the power receiving side. Inthe following description, the efficiency of power transmission betweencoils on the power transmitting side and the power receiving side isalso referred to as an inter-coil efficiency.

The other method is a technique referred to as a magnetic resonancemethod. The magnetic resonance method is characterized in that, byutilizing a resonance phenomenon deliberately, the magnetic flux sharedby the power supplier and the power receiver is small. In the magneticresonance method, even for a small coefficient of junction, theinter-coil efficiency does not deteriorate provided that the Q factor(quality factor) is high. The Q factor is an indicator representing arelation between energy holding and energy losing in circuits includingthe coils on the power transmitting side and the power receiving side.That is to say, the Q factor is an indicator representing the strengthof resonance of a resonant circuit. In other words, the magneticresonance method offers a merit that the axis of the coil on the powerreceiving side does not have to be adjusted to the axis of the coil onthe power transmitting side. Other merits include a high degree offreedom in selecting the positions of the power transmitting side andthe power receiving side as well as a high degree of freedom in settingthe distance between the power transmitting side and the power receivingside.

One of important elements in the non-contact power transmission systemis a countermeasure to be taken against heat dissipated by a metallicforeign substance. When electric power is supplied from a powertransmitting side to a power receiving side by adoption of a non-contacttechnique not limited to the electromagnetic induction method or themagnetic resonance method, a metal may exist between the powertransmitting side and the power receiving side. In this case, an eddycurrent may flow in the metal so that it is feared that the metaldissipates heat. As a countermeasure to be taken against the heatdissipated by the metal, there have been proposed a number of techniquesfor detecting such a metallic foreign substance. For example, techniquesmaking use of a light sensor or a temperature sensor are known. However,a method for detecting a metal by making use of a sensor is expensive ifthe power supplying range is wide as is the case with the magneticresonance method. In addition, if a temperature sensor is used forexample, a result output by the temperature sensor is dependent on thethermal conductivity of the surroundings of the sensor. Thus, designrestrictions are imposed on equipment on the power transmitting side andthe power receiving side.

In order to solve the problems described above, there has been proposeda technique for determining whether or not a metallic foreign substanceexists between the power transmitting side and the power receiving sidethrough examination of parameter changes caused by existence of themetallic foreign substance. The changes of parameters typically includechanges in current and changes in voltage. By adoption of such atechnique, it is no longer necessary to impose design restrictions onequipment on the power transmitting side and the power receiving side.In addition, the cost can be reduced. As described in Japanese PatentLaid-open No. 2008-206231 (hereinafter referred to as Patent Document 1)for example, there has been proposed a technique for detecting ametallic foreign substance through examination of the degree ofmodulation in transmission between the power transmitting side and thepower receiving side. That is to say, a metallic foreign substance isdetected by examining information on amplitude changes and phasechanges. In addition, as described in Japanese Patent Laid-open No.2001-275280 (hereinafter referred to as Patent Document 2), there hasbeen proposed a technique for detecting a metallic foreign substancethrough examination of an eddy-current loss. This technique is alsoreferred to as a foreign-substance detection method based on a DC-DCefficiency.

SUMMARY

However, the techniques disclosed in Patent Documents 1 and 2 do notconsider effects of a metallic case used on the power receiving side. Itis quite within the bounds of possibility that ordinary mobile equipmentreceiving electric power on the power receiving side makes use of somemetals such as a metallic case and metallic components. In such a case,it is difficult to determine whether a change of a parameter has beencaused by an effect of the metallic case or the like or has been causedby the existence of a metallic foreign substance. In the case of thetechnique disclosed in Patent Document 2 for example, it is difficult todetermine whether an eddy-current loss has been incurred in the metalliccase of the mobile equipment or incurred due to the existence of ametallic foreign substance between the power transmitting side and thepower receiving side. Thus, as is obvious from the above descriptions,the techniques disclosed in Patent Documents 1 and 2 cannot be said tobe techniques capable of detecting a metallic foreign substance with ahigh degree of precision.

The present disclosure has been made in order to solve the problemsdescribed above. It is desirable to increase the precision of detectionof a metallic foreign substance existing between the power transmittingside and the power receiving side.

In accordance with an embodiment of the present disclosure, there isprovided a detection apparatus including: a resonant circuit providedwith a Q-factor measurement coil and one or more capacitors to serve asa circuit for receiving pulses; a response-waveform detecting sectionconfigured to detect the waveform of a response output by the resonantcircuit in response to the pulses; and a Q-factor measuring sectionconfigured to measure a Q factor of the resonant circuit from theresponse waveform detected by the response-waveform detecting section.

In accordance with another embodiment of the present disclosure, thereis provided a power receiving apparatus including: a power receivingcoil electromagnetically coupled to an external apparatus; a powerreceiving section configured to receive electric power from the externalapparatus through the power receiving coil; a resonant circuit providedwith a Q-factor measurement coil and one or more capacitors to serve asa circuit for receiving pulses; a response-waveform detecting sectionconfigured to detect the waveform of a response output by the resonantcircuit in response to the pulses; and a Q-factor measuring sectionconfigured to measure a Q factor of the resonant circuit from theresponse waveform detected by the response-waveform detecting section.

In accordance with still another embodiment of the present disclosure,there is provided a non-contact power transmission system including: apower transmitting apparatus configured to transmit electric power byadoption of a non-contact transmission technique; and a power receivingapparatus configured to receive the electric power from the powertransmitting apparatus, wherein the power receiving apparatus includes apower receiving coil electromagnetically coupled to a power transmittingcoil of the power transmitting apparatus, a power receiving sectionconfigured to receive electric power from the power transmittingapparatus through the power receiving coil, a resonant circuit providedwith a Q-factor measurement coil and one or more capacitors to serve asa circuit for receiving pulses, a response-waveform detecting sectionconfigured to detect the waveform of a response output by the resonantcircuit in response to the pulses, and a Q-factor measuring sectionconfigured to measure a Q factor of the resonant circuit from theresponse waveform detected by the response-waveform detecting section.

In accordance with a further embodiment of the present disclosure, thereis provided a detection method including: applying pulses to a resonantcircuit provided with a Q-factor measurement coil and one or morecapacitors; driving a response-waveform detecting section to detect thewaveform of a response output by the resonant circuit in response to thepulses; and driving a Q-factor measuring section to measure a Q factorof the resonant circuit from the response waveform detected by theresponse-waveform detecting section.

In accordance with the present disclosure, by making use of a simpleconfiguration, it is possible to increase the precision of detection ofa metallic foreign substance existing between the power transmittingside and the power receiving side.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram roughly showing a typical detection circuit fordetecting a metallic foreign substance by measurement of a Q factor;

FIG. 2 is a diagram showing a graph representing a typical frequencycharacteristic of a voltage output by a series resonant circuit;

FIG. 3 is a diagram roughly showing a typical detection circuitaccording to a first embodiment of the present disclosure;

FIG. 4 is a block diagram showing a typical internal configuration of amicrocomputer shown in FIG. 3;

FIG. 5 is a diagram showing a simulation circuit constructed as a modelof the detection circuit shown in FIG. 3;

FIGS. 6A to 6E are a plurality of diagrams showing typical waveformsobtained at a variety of measurement points of the simulation circuitwith no metallic foreign substance under a first condition, that is, acondition with a Q factor of 100 and a repetition period of 2 ms;

FIG. 6A is an enlarged diagram showing the waveform of a pulse generatedby a pulse generator;

FIG. 6B is a diagram showing a train of pulses generated by the pulsegenerator;

FIG. 6C is a diagram showing a frequency-domain response to the pulsetrain;

FIG. 6D is an enlarged diagram showing a frequency-domain response tothe pulse train;

FIG. 6E is a diagram showing the frequency-domain response waveform of avoltage appearing at the two terminals of a capacitor shown in FIG. 5;

FIGS. 7A to 7E are a plurality of diagrams showing typical waveformsobtained at a variety of measurement points of the simulation circuitwith no metallic foreign substance under a second condition, that is, acondition with a Q factor of 100 and a repetition period of 10 ms;

FIG. 7A is an enlarged diagram showing the waveform of a pulse generatedby the pulse generator;

FIG. 7B is a diagram showing a train of pulses generated by the pulsegenerator;

FIG. 7C is a diagram showing a pulse train in the frequency domain;

FIG. 7D is a diagram showing a pulse train in the frequency domain byenlarging the inside of each pulse;

FIG. 7E is a diagram showing the frequency-domain response waveform of avoltage appearing at the two terminals of the capacitor shown in FIG. 5;

FIGS. 8A and 8B are a plurality of diagrams showing typical waveforms ofa voltage appearing at the two terminals of a capacitor for a Q factorof 100 and a repetition period of 10 ms;

FIG. 8A is a diagram showing a time-domain response waveform;

FIG. 8B is a diagram showing a frequency-domain response waveform;

FIGS. 9A and 9B are a plurality of diagrams showing typical waveforms ofa voltage appearing at the two terminals of a capacitor for a Q factorof 50 and a repetition period of 10 ms;

FIG. 9A is a diagram showing a time-domain response waveform;

FIG. 9B is a diagram showing a frequency-domain response waveform;

FIG. 10 is a circuit diagram roughly showing a power receiving apparatusprovided by a second embodiment of the present disclosure to serve as atypical apparatus to which the detection circuit is applied;

FIG. 11 is a diagram roughly showing a typical detection circuitaccording to a third embodiment of the present disclosure; and

FIG. 12 is a diagram roughly showing a typical detection circuitaccording to a fourth embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present disclosure are explained by referring to thediagrams as follows. It is to be noted that, throughout the diagrams andthis specification, configuration elements having functions essentiallyidentical with each other and/or having configurations essentiallyidentical with each other are denoted by the same reference numeral, andduplicate descriptions are omitted.

It is to be noted that the description of the embodiments is dividedinto topics arranged in the following order:

1: Introduction

2: First Embodiment (Signal source: Example using a pulse generator)

3: Second Embodiment (Detection circuit: Typical application to a powerreceiving apparatus)

4: Third Embodiment (Detection circuit: Example employing anenvelop-line detecting circuit)

5: Fourth Embodiment (Q-factor measurement: Typical Q-factor measurementusing the number of vibrations)

6: Fifth Embodiment (Q-factor measurement: Typical Q-factor measurementbased on a voltage V₂ in a predetermined range)

7: Sixth Embodiment (Q-factor measurement: Typical Q-factor measurementbased on a time limit even for the voltage V₂ not in a predeterminedrange)

8: Others

1: Introduction

Detection of a Metallic Foreign Substance by Measurement of the Q Factor

In order to detect a metallic foreign substance, which exists betweenthe power transmitting side and the power receiving side, with a highdegree of precision, there has been conceived a method for determiningwhether or not a metallic foreign substance exists at a position closeto a coil included in a resonant circuit on the power receiving side asa coil coupled magnetically with an external component on the powertransmitting side on the basis of a measured Q factor (quality factor)of the circuit. It is possible to determine whether or not such ametallic foreign substance exists because, as the metallic foreignsubstance approaches the resonant circuit, the Q factor of the circuitdecreases.

The Q factor of a resonant circuit is an indicator representing arelation between energy holding and energy losing in the resonantcircuit. In general, the Q factor is used as a value representing thesharpness of the peak of the resonance curve of the resonant circuit. Inother words, the Q factor is used as a value representing the degree ofthe resonance of the resonant circuit.

The detection of the metallic foreign substance is performed on acircuit existing between the power transmitting side and the powerreceiving side and including an unintended coil and a conductor such asa metal. The technical term “conductor” used in this specification meansa conductor in the broad sense of the term. Thus, the technical term“conductor” used in this specification can also be interpreted as asemiconductor. In the following description, an operation to detect acircuit including such a coil and a conductor such as a metal isreferred to as detection of conductors and the like.

A typical detection circuit for detecting a metallic foreign substanceby measurement of the Q factor is explained as follows.

FIG. 1 is a diagram roughly showing a typical detection circuit 1 fordetecting a metallic foreign substance by measurement of the Q factor ofa resonant circuit.

As shown in the figure, the detection circuit 1 includes a Q-factormeasurement coil 11, a capacitor 12, a signal source 13 and an ADC 16which is an analog-to-digital converter. The detection circuit 1 shownin FIG. 1 is a rough circuit referred to in explanation of an outline ofan operation to detect a metallic foreign substance by measuring the Qfactor of a resonant circuit which includes the Q-factor measurementcoil 11 and the capacitor 12.

In the detection circuit 1, the Q-factor measurement coil 11 and thecapacitor 12 are connected to each other in series to form the resonantcircuit enclosed by a dashed line. The inductance of the Q-factormeasurement coil 11 and the capacitance of the capacitor 12 are adjustedso that the resonant circuit resonates at a measurement frequency whichis referred to as a resonance frequency. In the following description,the inductance of the Q-factor measurement coil 11 and the capacitanceof the capacitor 12 are also referred to as an L value and a C valuerespectively. The signal source 13 is connected to the resonant circuitwhich includes the Q-factor measurement coil 11 and the capacitor 12 asdescribed above. A variable-frequency sinusoidal-signal generator 14included in the signal source 13 generates a sinusoidal signal having avariable frequency and supplies the signal to the resonant circuit. Aresistor 15 in the signal source 13 represents the internal resistanceof the variable-frequency sinusoidal-signal generator 14 or the outputimpedance of the variable-frequency sinusoidal-signal generator 14.

Analog signals generated at measurement points in the resonant circuitreceiving the sinusoidal signal are supplied to the ADC 16 forconverting the analog signals into a digital signal. Then, the Q factorof the resonant circuit is measured by making use of the digital signaloutput by the ADC 16 as a result of the analog-to-digital conversion. Itis to be noted that the detection circuit 1 has a power-supply sectionnot shown in the figure. The power-supply section supplies electricpower to components employed in the detection circuit 1. As describedabove, the components employed in the detection circuit 1 include thesignal source 13 and the ADC 16.

In the measurement of the Q factor of the resonant circuit, first ofall, frequency sweeping is carried out on the sinusoidal signal appliedto the resonant circuit in order to find a resonance frequency f₀ atwhich a voltage output by the resonant circuit attains a maximum value.Then, at the resonance frequency f₀, a voltage V_(I) and a voltage V_(C)are measured and the measured voltages are used in the measurement ofthe Q factor. As shown in FIG. 1, the voltage V_(I) is a voltageappearing at a connection point between the Q-factor measurement coil 11and the signal source 13 whereas the voltage V_(C) is a voltageappearing at a connection point between the Q-factor measurement coil 11and the capacitor 12. Typically, an LCR meter is used as a Q-factormeasuring apparatus in the measurement of the Q factor.

The Q factor of the resonant circuit is expressed by Equation 1 givenbelow. In the equation, reference notation V_(I) denotes a voltageappearing at a connection point between the Q-factor measurement coil 11and the signal source 13 whereas reference notation V_(C) denotes avoltage appearing at a connection point between the Q-factor measurementcoil 11 and the capacitor 12 as described above. On the other hand,reference notation R denotes a series resistance at the resonancefrequency f₀.

$\begin{matrix}{Q = {{\frac{1}{R}\sqrt{\frac{L}{C}}} = \frac{V_{C}}{V_{I}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

As is obvious from the above equation, the voltage V_(C) is about Qtimes the voltage V_(I). As is commonly known, the series resistance Rand the inductance L which are used in Equation 1 change when a metalapproaches the resonant circuit or change due to an effect of an eddycurrent generated in the metal. When a metallic piece approaches theQ-factor measurement coil 11 for example, the effective seriesresistance R much increases and, thus, the Q factor decreases. That isto say, due to an effect of a metal existing in the vicinity of theQ-factor measurement coil 11, the Q factor of the resonant circuit andthe resonance frequency of the resonant circuit change much. Thus, bydetecting these changes, it is possible to detect a metallic pieceexisting in the vicinity of the Q-factor measurement coil 11. Thepresent disclosure is applied to detection of a metallic foreignsubstance inserted between first and secondary sides which are the powertransmitting side and the power receiving side respectively.

By making use of a Q-factor change described above to detect a metallicforeign substance with a high degree of precision, the metallic foreignsubstance can be removed without regard to whether the adopted method isthe electromagnetic induction method or the magnetic resonance method.In particular, the Q factor of the resonant circuit employing a Q-factormeasurement coil in equipment on the power receiving side serving as thesecondary side can be used as a parameter which is sensitive to ametallic foreign substance because a relation between the position ofthe metallic case of the equipment on the power receiving side and theposition of the Q-factor measurement coil is all but fixed. Thus, aneffect of the metallic case on the Q-factor measurement coil can beeliminated. That is to say, in comparison with the power transmittingside, the Q factor of a resonant circuit provided on the power receivingside is proper for high-precision detection of a metallic foreignsubstance.

In addition, the Q factor of a resonant circuit can be computed byadoption of a half-band width method.

The half-bandwidth method is based on Equation 2 given below. As isobvious from the equation, the Q factor is found from the resonancefrequency f₀, a relatively low frequency f_(L) and a relatively highfrequency f_(H). As explained earlier, the resonance frequency f₀ is afrequency at which the amplitude of a voltage output by the resonantcircuit attains a maximum value also referred to as a peak value. Theresonance frequency f₀ is found by execution of frequency sweeping onthe sinusoidal signal applied to the resonant circuit. As shown in FIG.2, the relatively low frequency f_(L) is a frequency lower than theresonance frequency f₀ whereas the relatively high frequency f_(H) is afrequency higher than the resonance frequency f₀. At the relatively lowfrequency f_(L) and the relatively high frequency f_(H), the amplitudeof the voltage output by the resonant circuit decreases from the peakvalue by 3 dB to a value equal to (1/√2) times the peak value. To bemore specific, in accordance with Equation 2, the Q factor is found bydividing the resonance frequency f₀ by a bandwidth of (f_(H)−f_(L))between the frequencies f_(H) and f_(L) at which the amplitude of thevoltage output by the resonant circuit decreases from the peak value by3 dB to a value equal to (1/√2) times the peak value.

$\begin{matrix}{Q = \frac{f_{0}}{f_{H} - f_{L}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

It is to be noted that the series resonant circuit described above is nomore than a typical resonant circuit. Explanation of a parallel resonantcircuit can be obtained by reversing some phrases in the aboveexplanation. That is to say, in the same way as the series resonantcircuit, the Q factor is found from the resonance frequency f₀, arelatively low frequency f_(L) and a relatively high frequency f_(H). Inthis case, however, the resonance frequency f₀ is a frequency at whichthe amplitude of a voltage output by the resonant circuit attains aminimum value. To be more specific, in accordance with Equation 2, the Qfactor is found by dividing the resonance frequency f₀ by a bandwidth of(f_(H)−f_(L)) between the frequencies f_(H) and f_(L) at which theamplitude of the voltage output by the parallel resonant circuitincreases from the minimum value by 3 dB to a value equal to (√2) timesthe minimum value.

In the case of either of the Q-factor measurement methods, however, theresonance frequency f₀ is found by execution of frequency sweeping onthe sinusoidal signal applied to the resonant circuit in the course ofthe Q-factor measurement. It is thus necessary to provide avariable-frequency sinusoidal-signal generator having an excellentfrequency resolution. In addition, since the frequency sweeping may becarried out, it takes time to perform the Q-factor measurement.

On top of that, in the case of the former method, the voltage V_(I) isabout 1/Q times the voltage V_(C). Thus, since the voltage V_(I) has alow level, it is difficult to measure the Q factor with a high degree ofaccuracy. That is to say, the precision of the measurement of the Qfactor is low.

In order to solve the problem described above, the Q factor is measuredby execution of processing based on pulses applied to the resonantcircuit. If pulses are used in place of a sinusoidal signal, it is nolonger necessary to provide a variable-frequency sinusoidal-signalgenerator having an excellent frequency resolution.

2: First Embodiment

Typical Configuration of a Detection Circuit

FIG. 3 is a diagram roughly showing a typical detection circuit 10 towhich the detection apparatus according to a first embodiment of thepresent disclosure is applied. The detection circuit 10 shown in FIG. 3is a circuit shown roughly in the explanatory diagram referred to in thefollowing description of an outline of an operation to detect a metallicforeign substance by measuring the Q factor. In FIG. 3, an elementhaving a function and/or a configuration which are essentially identicalwith those of its counterpart shown in FIG. 1 is denoted by the samereference numeral as the counterpart. In addition, the explanation ofthe identical element is omitted in order to avoid duplications of thedescription of the element.

The detection circuit 10 according to this embodiment is provided with asignal source 21 replacing the signal source 13 employed in thedetection circuit 1 shown in FIG. 1.

The signal source 21 is connected to a resonant circuit enclosed by adashed line. In the resonant circuit, a Q-factor measurement coil 11 anda capacitor 12 are connected to each other in series. The signal source21 includes a pulse generator 22 for generating pulses at periodsdetermined in advance. A resistor 23 in the signal source 21 representsthe internal resistance of the pulse generator 22 or the outputimpedance of the pulse generator 22.

In addition, the detection circuit 10 also includes an ADC 16 and amicrocomputer 17. The ADC 16 is a typical response-waveform detectingsection for detecting the waveform of a response output by the resonantcircuit in response to the pulse signal received from the signal source21. On the other hand, the microcomputer 17 receives a digital signalfrom the ADC 16. The remaining configuration of the detection circuit 10is identical with that of the detection circuit 1.

It is to be noted that the detection circuit 10 has a power-supplysection not shown in the figure as with the case of the detectioncircuit 1. The power-supply section supplies electric power tocomponents employed in the detection circuit 10. As described above, thecomponents employed in the detection circuit 10 include the signalsource 21, the ADC 16 and the microcomputer 17.

The operation of the detection circuit 10 is explained briefly asfollows.

Pulses output by the pulse generator 22 employed in the signal source 21are applied to the resonant circuit. A voltage appearing at theconnection point between the Q-factor measurement coil 11 and thecapacitor 12 is sequentially fetched and supplied to the ADC 16. Thevoltage appearing at the connection point between the Q-factormeasurement coil 11 and the capacitor 12 is a voltage appearing betweenthe two terminals of the capacitor 12. The ADC 16 converts the analogsignal of the voltage into a digital signal in order to obtain thetime-domain waveform of a response to the pulses applied to the resonantcircuit. The ADC 16 supplies the time-domain response waveform to themicrocomputer 17 which then processes the waveform in order to computethe Q factor. The microcomputer 17 finally detects existence of ametallic foreign substance on the basis of the computed Q factor.

The following description explains a configuration and an operationwhich are related to processing carried out by the microcomputer 17 inorder to detect a metallic foreign substance in accordance with thisembodiment.

FIG. 4 is a block diagram showing a typical internal configuration ofthe microcomputer 17.

As shown in the figure, the microcomputer 17 according to thisembodiment is configured to include a Q-factor measuring section 17A, adetermination section 17B, a memory 17C and a control section 17D. Themicrocomputer 17 is a typical processing apparatus. The microcomputer 17measures the Q factor of the resonant circuit and controls the detectioncircuit 10 or the entire equipment provided with the detection circuit10.

The Q-factor measuring section 17A is a typical Q-factor measuringsection. The Q-factor measuring section 17A carries out processing to bedescribed later on the digital voltage signal received from the ADC 16in order to find the Q factor. The Q-factor measuring section 17Asupplies the Q factor to the determination section 17B. The amplitude ofthe digital voltage signal received from the ADC 16 represents thevibration of the signal. The vibration of the digital voltage signal isshifted or attenuated with the lapse of time. The Q-factor measuringsection 17A computes the Q factor on the basis of the time-wise shift ofthe vibration of the digital voltage signal.

The determination section 17B is a typical determination section forcomparing the Q factor received from the Q-factor measuring section 17Awith a reference value determined in advance in order to determinewhether or not a metallic foreign substance exists in the vicinity ofthe Q-factor measurement coil 11. The determination section 17B suppliesthe result of the determination to the control section 17D. By comparingthe Q factor of the resonant circuit including the Q-factor measurementcoil 11 with the reference value as described above, it is possible toinfer electromagnetic coupling between the Q-factor measurement coil 11and the external world. Thus, by properly setting the reference value,it is possible to precisely determine whether or not a metallic foreignsubstance exists between the Q-factor measurement coil 11 and theexternal world.

The memory 17C is a typical nonvolatile storage section. The memory 17Cis used for storing the reference value of the Q factor of the resonantcircuit employing the Q-factor measurement coil 11 for every frequency.The reference value is a value determined in advance for a state inwhich nothing exists in the vicinity of the Q-factor measurement coil 11or for a state in which nothing exists between the Q-factor measurementcoil 11 and an external coil. In addition, the memory 17C can also beused for storing an ID number assigned to every equipment employing thedetection circuit 10 to serve as information used for identifying theequipment. On top of that, the memory 17C can also be used for storingother information such as an ID number acquired from external equipment.

The control section 17D is a typical control section for generatingcontrol signals according to a determination result received from thedetermination section 17B and making use of the control signals tocontrol, among others, the entire detection circuit 10 and non-contactpower transmission carried out by execution of communications withequipment employing an external coil.

The figure shows a typical configuration in which the Q-factor measuringsection 17A, the determination section 17B and the control section 17Dare included in the microcomputer 17. It is to be noted, however, thatone or more combinations of any ones of the Q-factor measuring section17A, the determination section 17B and the control section 17D can alsobe typically included in another processing apparatus in adistributed-processing environment or the like.

The pulses have a simple rectangular waveform in the time domain. If thesimple rectangular waveform in the time domain is transformed into awaveform in the frequency domain, however, the waveform in the frequencydomain has a spectrum spread over a wide range. Thus, by properlyselecting the waveform of the pulses, it is possible to obtain aspectrum having a comb shape with approximately the same amplitude inthe vicinity of the resonance frequency. Accordingly, by applying apulse to the resonant circuit and observing the response to the pulse,it is possible to obtain the frequency characteristic of the impedanceof the resonant circuit. In addition, the Q factor can also be computedby carrying out the processing in the time domain.

Simulation Results

The following description explains results obtained by simulating thedetection circuit 10.

FIG. 5 is a diagram showing a simulation circuit constructed as a modelof the detection circuit 10.

The simulation circuit shown in FIG. 5 includes a pulse generator 33 andan LC resonant circuit corresponding to the block enclosed by a dashedline in FIG. 3. The LC resonant circuit resonates at pulse waves havinga frequency of 100 Hz. The LC resonant circuit includes a Q-factormeasurement coil 31 and a capacitor 32. As a first condition, the Qfactor of the LC resonant circuit is set at 100 and the pulse generator33 is set to generate pulse waves having an amplitude of 1 V and a pulsewidth of 1 μsec for a repetition period of 2 msec.

The effective resistance R of the LC resonant circuit is expressed bythe equation R=√(Ls/Cs)/Qs where reference notation Ls denotes aninductance expressed in terms of H as the inductance of the Q-factormeasurement coil 31, reference notation Cs denotes a capacitanceexpressed in terms of F as the capacitance of the capacitor 32 andreference notation Qs denotes the Q factor of the LC resonant circuit.

For a First Condition

FIGS. 6A to 6E are a plurality of diagrams showing typical waveformsobtained at a variety of measurement points of the simulation circuitshown in FIG. 5 with no metallic foreign substance under the firstcondition, that is, a condition with a Q factor of 100 and a repetitionperiod of 2 ms. To be more specific, FIG. 6A is an enlarged diagramshowing the waveform of a pulse generated by the pulse generator 33shown in FIG. 5 whereas FIG. 6B is a diagram showing a train of pulsesgenerated by the pulse generator 33. FIG. 6C is a diagram showing afrequency-domain response to the pulse train whereas FIG. 6D is anenlarged diagram showing a frequency-domain response to the pulse train.On the other hand, FIG. 6E is a diagram showing the frequency-domainresponse waveform of a voltage appearing at the two terminals of thecapacitor 32 shown in FIG. 5.

As shown in FIG. 6B, the pulse train generated by the pulse generator 33is a train of pulses each having an amplitude of 1 V and a pulse widthof 1 μsec. The pulse train is generated for a repetition period of 2msec. FIG. 6A shows the waveform of a pulse generated by the pulsegenerator 33 by expanding the time axis of the pulse train shown in FIG.6B from the msec order to the μsec order.

The frequency-domain response shown in FIG. 6C is obtained bytransforming the time-domain pulse waveform shown in FIG. 6A into awaveform in the frequency domain. If the frequency axis of thefrequency-domain response shown in FIG. 6C is expanded, it is possibleto obtain a spectrum having a comb shape with an approximately uniformamplitude of 1 mV in the vicinity of the resonance frequency of 100 kHzas shown in FIG. 6D.

Let a pulse wave having such a spectrum be applied to the LC resonantcircuit and let the time-domain response waveform of a voltage appearingat the terminals of the capacitor 32 be transformed into a waveform inthe frequency domain. In this case, the result of the transformation isthe frequency-domain response waveform shown in FIG. 6E. Thetime-to-frequency transformation processing is carried out by the ADC 16employed in the detection circuit 10. As an alternative, in place of theADC 16, the Q-factor measuring section 17A employed in the microcomputer17 may carry out the time-to-frequency transformation processing.

In the case of pulse waves satisfying the first condition, that is, acondition with a Q factor of 100 and a repetition period of 2 ms, thepulse interval is short and the amplitude (or an average electric power)obtained as a result of a frequency analysis is large but the frequencyresolution is poor.

For a Second Condition

FIGS. 7A to 7E are a plurality of diagrams showing typical waveformsobtained at a variety of measurement points of the simulation circuitshown in FIG. 5 with no metallic foreign substance under a secondcondition, that is, a condition with a Q factor of 100 and a repetitionperiod of 10 ms. To be more specific, FIG. 7A is an enlarged diagramshowing the waveform of a pulse generated by the pulse generator 33shown in FIG. 5 whereas FIG. 7B is a diagram showing a train of pulsesgenerated by the pulse generator 33. FIG. 7C is a diagram showing afrequency-domain response to the pulse train whereas FIG. 7D is anenlarged diagram showing a frequency-domain response C to the pulsetrain. On the other hand, FIG. 7E is a diagram showing thefrequency-domain response waveform of a voltage appearing at the twoterminals of the capacitor 32 shown in FIG. 5.

As shown in FIG. 7B, the pulse train generated by the pulse generator 33is a train of pulses each having an amplitude of 1 V and a pulse widthof 1 μsec. The pulse train is generated for a repetition period of 10msec. FIG. 7A shows the waveform of a pulse generated by the pulsegenerator 33 by expanding the time axis of the pulse train shown in FIG.7B from the msec order to the μsec order.

The pulse train shown in FIG. 7C is obtained by transforming thetime-domain pulse waveform shown in FIG. 7A into a waveform in thefrequency domain. If the frequency axis of the frequency-domain responseto the pulse train shown in FIG. 7C is expanded, it is possible toobtain a spectrum having a comb shape with an approximately uniformamplitude of 200 μV in the vicinity of the resonance frequency of 100kHz as shown in FIG. 7D.

Let a pulse wave having such a spectrum be applied to the LC resonantcircuit and let the time-domain response waveform of a voltage appearingat the terminals of the capacitor 32 be transformed into a waveform inthe frequency domain. In this case, the result of the transformation isthe frequency-domain response waveform shown in FIG. 7E.

In the case of pulse waves satisfying the second condition, that is, acondition with a Q factor of 100 and a repetition period of 10 ms, thepulse interval is long and the amplitude (or an average electric power)obtained as a result of a frequency analysis is small but the frequencyresolution is excellent.

As described above, the amplitude obtained as a result of a frequencyanalysis and the frequency resolution can be changed by not only theamplitude of a pulse wave, but also the pulse interval (or the pulseperiod). The amplitude and the frequency resolution are in a tradeoffrelation to each other. It is desirable that a person in charge ofmeasurements properly selects a large amplitude or an excellentfrequency resolution in accordance with the object of measurement.

In both the first and second conditions, the Q factor is set at 100. Inaccordance with Equation 2, the Q factor is expressed by the equationQ=f₀/(f_(H)−f_(L)) where the expression (f_(H)−f_(L)) represents thewidth of a frequency band. At the relatively low frequency f_(L) and therelatively high frequency f_(H) which serve as the edge frequencies ofthe band, the amplitude of the voltage output by the resonant circuitdecreases from the peak value attained at the resonance frequency f₀ by3 dB to a value equal to (1/√2=0.7071) times the peak value. From thefrequency-domain response waveforms shown in FIGS. 6E and 7E, therelatively high frequency f_(H), the resonance frequency f₀ and therelatively low frequency f_(L) are found to be 100.5 kHz, 100 kHz and99.5 kHz respectively. Thus, Q=100 kHz/(100.5 kHz−99.5 kHz)=100 which isa result obtained on the assumption that no metallic foreign substanceexists.

Q-Factor Measurement Based on Analysis Results

Next, the following description explains a method for measuring the Qfactor on the basis of results of analyses carried out in the time andfrequency domains after the pulses described above have been applied tothe LC resonant circuit shown in FIG. 5.

FIGS. 8A and 8B are a plurality of diagrams showing typical waveforms ofa voltage appearing at the two terminals of the capacitor 32 for a Qfactor of 100 and a repetition period of 10 ms. To be more specific,FIG. 8A is a diagram showing a time-domain response waveform whereasFIG. 8B is a diagram showing a frequency-domain response waveform.

On the assumption that no metallic foreign substance exists, the LCresonant circuit used in the analyses has a Q factor of 100 whereas thepulse train supplied to the circuit has a pulse amplitude of 1 V, apulse width of 1 μsec and a pulse repetition period of 10 msec.

As shown in FIG. 8A, after pulses have been applied to the LC resonantcircuit, the time-domain voltage appearing at the two terminals of thecapacitor 32 is gradually attenuated. In addition, as shown in FIG. 8B,the frequency-domain voltages appearing at the two terminals of thecapacitor 32 have a peak at the resonance frequency and an amplitudewhich is gradually attenuated as the frequency deviates from theresonance frequency. The larger the deviation of a frequency from theresonance frequency, the smaller the amplitude at the frequency.

Time Domain

The Q factor of the LC resonant circuit is expressed by Equation 3 givenbelow. In this equation, reference notation f denotes the resonancefrequency of the resonant circuit. Reference notation V₁ is the voltageappearing at the two terminals of the capacitor 32 at a time t₁ or avoltage observed at a measurement point m4 on the voltage waveform. Bythe same token, reference notation V₂ is the voltage appearing at thetwo terminals of the capacitor 32 at a time t₂ or a voltage observed ata measurement point m5 on the time-domain response waveform. Themeasurement point m5 is a point lagging behind the measurement point m4.

$\begin{matrix}{Q = {\pi\;{f \cdot \frac{t_{2} - t_{1}}{1{n\left( \frac{V_{1}}{V_{2}} \right)}}}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

The following description briefly explains a process of deriving theequation for finding the Q factor from the resonance frequency andamplitudes (that is, voltages) observed at two times on the time-domainresponse waveform.

First of all, an energy supplied to the resonant circuit is expressed byEquation 4 as follows.Energy E=|a(t)|² ,a(t)=A·e ^(−Γt) ·e ^(jωt)Vibration term:e ^(jωt)(|e ^(jωt)|=1)  [Equation 4]

Next, an electric power is taken into consideration. In order to makethe explanation simple, the vibration term is omitted hereafter toresult in Equation 5 given below. Equation 5 represents only theenvelop-line term.a(t)=A·e ^(−Γt)  [Equation 5]∴E=A ² ·e ^(−2Γt)  [Equation 6]

Since an electric power P is an energy consumed in a unit time, theelectric power P can be expressed by Equation 7 as follows.

$\begin{matrix}{P = {{{- \frac{d}{dt}}E} = {{{- \frac{d}{dt}}\left( {A^{2} \cdot e^{{- 2}\Gamma\; t}} \right)} = {{2{\Gamma\left( {A^{2} \cdot e^{{- 2}\Gamma\; t}} \right)}} = {2\Gamma\; E}}}}} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

The Q factor is defined as a ratio of an internal energy of a resonancesystem to an energy lost by the resonance system in one period. In thiscase, the following equation can be derived by substituting Equation 7for the electric power P into the defined ratio as follows.

$\begin{matrix}{{Q \equiv \frac{{internal}\mspace{14mu}{energy}\mspace{14mu}{of}\mspace{14mu}{resonance}\mspace{14mu}{system}}{{energy}\mspace{14mu}{lost}\mspace{14mu}{by}\mspace{14mu}{resonance}\mspace{14mu}{system}\mspace{14mu}{in}\mspace{14mu} 1\mspace{14mu}{rad}}} = {\frac{E}{P \cdot \frac{1}{\omega}} = {\frac{\omega\; E}{P} = {\frac{\omega\; E}{2\Gamma\; E} = \frac{\omega}{2\Gamma}}}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack \\{\mspace{79mu}{{\therefore\Gamma} = \frac{\omega}{2Q}}} & \left\lbrack {{Equation}\mspace{14mu} 9} \right\rbrack \\{\mspace{79mu}{{\therefore{a(t)}} = {A \cdot e^{{- \frac{\omega}{2Q}}t}}}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

Then, Equations 11 to 13 are derived from Equation 10 and, finally,Equation 3 is obtained.

$\begin{matrix}{\frac{{a\left( t_{1} \right)}}{{a\left( t_{2} \right)}} = {\frac{A \cdot e^{{- \frac{\omega}{2Q}}t_{1}}}{A \cdot e^{{- \frac{\omega}{2Q}}t_{2}}} = e^{{- \frac{\omega}{2Q}}{({t_{1} - t_{2}})}}}} & \left\lbrack {{Equation}\mspace{14mu} 11} \right\rbrack \\{{1n\left\{ \frac{{a\left( t_{1} \right)}}{{a\left( t_{2} \right)}} \right\}} = {\frac{\omega}{2Q}\left( {t_{2} - t_{1}} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack \\{{\therefore Q} = {{\frac{\omega}{2} \cdot \frac{t_{2} - t_{1}}{1n\left\{ \frac{{a\left( t_{1} \right)}}{{a\left( t_{2} \right)}} \right\}}} = {\pi\;{f \cdot \frac{t_{2} - t_{1}}{1n\left\{ \frac{{a\left( t_{1} \right)}}{{a\left( t_{2} \right)}} \right\}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack\end{matrix}$

Data for the measurement point m4 on the time-domain response waveformincludes t₁=3.010 μsec and V₁=0.616 V. By the same token, data for themeasurement point m5 on the time-domain response waveform includest₂=443.1 μsec and V₂=0.154 V. These pieces of data are substituted intoEquation 3 to find the Q factor of the LC resonant circuit. In thiscase, a Q factor of 99.71 is obtained. The Q factor is computed asfollows:Q factor=π·100×10³·(3.010×10⁻⁶−443.1×10⁻⁶)/1n(0.616/0.154)=99.71Frequency Domain

Next, the Q factor is computed from the frequency-domain responsewaveform shown in FIG. 8B as follows.

FIG. 8B shows three measurement points m1, m2 and m3. The measurementpoint m1 corresponds to a peak value observed at the resonance frequencyof 100.0 kHz whereas the measurement points m2 and m3 each correspond toa voltage equal to 1/√2 (=0.7071) times the peak value. To put itconcretely, the measurement point m1 represents the resonance frequencyof 100.0 kHz and the peak value of 0.020 V. On the other hand, themeasurement point m2 represents a frequency of 99.5 kHz and a voltage of0.014 V whereas the measurement point m3 represents a frequency of 100.5kHz and a voltage of 0.014 V. In this case, the Q factor of the LCresonant circuit is found by making use of Equation 2 as follows.Q factor=100/(100.5−99.5)=100

The Q factor of 100 is about equal to the Q factor found from thetime-domain response waveform shown in FIG. 8A.

It is to be noted that, for the purpose of comparison with analysisresults shown in FIGS. 8A and 8B, the Q factor of the resonant circuitreceiving applied pulses was changed and the same analyses for the timedomain as well as the frequency domain were carried out.

FIGS. 9A and 9B are a plurality of diagrams showing typical waveforms ofa voltage appearing at the two terminals of the capacitor 32 for a Qfactor of 50 and a repetition period of 10 ms. To be more specific, FIG.9A is a diagram showing a time-domain response waveform whereas FIG. 9Bis a diagram showing a frequency-domain response waveform.

On the assumption that no metallic foreign substance exists, the LCresonant circuit used in the analyses has a Q factor of 50 and thespecification of the pulse applied to the circuit is the same as thatfor the case shown in FIGS. 8A and 8B.

As shown in FIG. 9A, after pulses have been applied to the LC resonantcircuit, the time-domain voltages appearing at the two terminals of thecapacitor 32 is attenuated faster than the case shown in FIG. 8A. Inaddition, as shown in FIG. 9B, the frequency-domain voltages appearingat the two terminals of the capacitor 32 have a peak at the resonancefrequency and an amplitude which is gradually attenuated as thefrequency deviates from the resonance frequency. However, thefrequency-domain response waveform shown in FIG. 9B is not so sharp asthe frequency-domain response waveform shown in FIG. 8B.

In accordance with the first embodiment described above, after pulseshave been applied to the resonant circuit, the Q factor can be foundwith a high degree of accuracy from either the time-domain responsewaveform or the frequency-domain response waveform. Therefore, ametallic foreign substance can be detected with a high degree ofprecision. In addition, it is not necessary to provide avariable-frequency sinusoidal-signal generator having a good frequencyresolution. That is to say, since a pulse generator for generating fixedpulse waves is adequate for the detection circuit to operate, theconfiguration of the detection circuit can be made simple.

In addition, if the resolution of the pulse wave in the frequency domainand the waveform fetching resolution in the frequency domain aresufficiently high, the precision of the pulse waveform is not required.

On top of that, repetitive works such as frequency sweeping are also notrequired. Thus, the measurement time is shortened substantially.

Moreover, the Q factor is measured from a voltage appearing at the twoterminals of a reactance element, making it unnecessary to measure asmall voltage applied to the entire resonant circuit. Thus, measurementscan be carried out with a high degree of precision.

It is possible to provide a configuration allowing the processing to becarried out on the basis of both the time-domain response and thefrequency-domain response and also allowing the time-domain response orthe frequency-domain response to be properly selected on a case-by-casebasis. In a typical configuration allowing the time-domain response orthe frequency-domain response to be properly selected on a case-by-casebasis, since the resonance frequency of a power receiving apparatus onceset on a planar power supplying base is conceived to hardly change, theresonance frequency is found from the frequency-domain response only inthe initial supplying of electric power. Then, in the subsequentsupplying of electric power, only the Q factor is computed from thetime-domain response.

By the way, the Q factor may be computed from the time-domain responseas described above. In this case, the time-domain response waveformundesirably includes also a signal having a frequency other than theresonance frequency. As described above, however, the precision of thecomputed Q factor is high. This is because the filtering of the resonantcircuit itself conceivably makes the resonance-frequency componentdominant.

3: Second Embodiment

A second embodiment implements typical application of the detectioncircuit 10 according to the first embodiment to a power receivingapparatus.

FIG. 10 is a circuit diagram roughly showing a typical non-contact powertransmission system including a power receiving apparatus 60 provided bythe second embodiment of the present disclosure to serve as an apparatusto which the detection circuit 10 is applied. In FIG. 10, an elementhaving a function and a configuration which are essentially identicalwith those of its counterpart shown in FIG. 3 is denoted by the samereference numeral as the counterpart. In addition, detailed explanationof each identical element is omitted.

As shown in FIG. 10, the non-contact power transmission system accordingto the second embodiment is configured to include a power transmittingapparatus 40 and the power receiving apparatus 60 which also has thefunction of the detection circuit 10. That is to say, the powerreceiving apparatus 60 includes a power receiving circuit 50 and thedetection circuit 10 shown in FIG. 3. As described before, the detectioncircuit 10 detects a metallic foreign substance by measuring the Qfactor of the detection resonant circuit employed in the detectioncircuit 10.

As shown in FIG. 10, the power transmitting apparatus 40 includes asignal source 43, a capacitor 41 and a power transmitting coil 42 whichis also referred to as a primary-side coil. The signal source 43includes a resistor 45 and a sinusoidal-power generator 44 forgenerating electric power having a sinusoidal waveform. The resistor 45included in the signal source 43 represents the internal resistance ofthe sinusoidal-power generator 44 or the output impedance of thesinusoidal-power generator 44.

In this embodiment, the capacitor 41 and the power transmitting coil 42are connected in series to the signal source 43 so that the capacitor 41and the power transmitting coil 42 form an apparatus series resonantcircuit. In addition, the capacitance of the capacitor 41 and theinductance of the power transmitting coil 42 are adjusted so that theapparatus series resonant circuit resonates at a resonance frequency atwhich electric power is to be transmitted to the power receiving circuit50. Also referred to as an electrostatic capacitance, the capacitance ofthe capacitor 41 is also called a C value in the following description.On the other hand, the inductance of the power transmitting coil 42 isalso referred to as an L value in the following description. The signalsource 43 and the capacitor 41 are included in a power transmittingsection of the power transmitting apparatus 40. The power transmittingsection transmits electric power to an external destination such as thepower receiving apparatus 60 by way of the power transmitting coil 42through radio transmission or non-contact transmission.

As described above, the power receiving apparatus 60 has two functions,that is, the function of the power receiving circuit 50 and the functionof the detection circuit 10. The power receiving circuit 50 serving as atypical power receiving section receives the electric power transmittedby the power transmitting apparatus 40 by non-contact transmission. Onthe other hand, the detection circuit 10 serving as a typical detectionsection detects a metallic foreign substance existing between the powerreceiving apparatus 60 and the power transmitting apparatus 40.

The power receiving circuit 50 includes a power receiving coil 51 alsoreferred to as a secondary-side coil, a capacitor 52, a rectificationcircuit 53 and a battery 54 which is also referred to as asecondary-side battery. The power receiving coil 51 and the capacitor 52form an apparatus series resonant circuit. The rectification circuit 53rectifies AC electric power into DC electric power. In addition to therectification, the rectification circuit 53 may also be configured tosmooth the DC electric power obtained as a result of the rectification.The battery 54 supplies electric power to a variety of sections includedin the power receiving apparatus 60. The battery 54 supplies electricpower to mainly the signal source 21 which employs the pulse generator22. In FIG. 10, the connection between the battery 54 and the signalsource 21 is shown as a solid line. However, connections between thebattery 54 and the other sections included in the power receivingapparatus 60 are not shown.

As described above, the power receiving circuit 50 includes a loadadjusting section 55. The load adjusting section 55 is connected inparallel to the apparatus resonant circuit consisting of the powerreceiving coil 51 and the capacitor 52 which are connected to each otherin series. A typical load adjusting section 55 includes a load and aswitch which are connected to each other in series. A typical example ofthe load is a resistor. In accordance with control executed by thecontrol section 17D employed in the microcomputer 17, the switch isturned on and off in order to connect the load to the power receivingcircuit 50 and disconnect the load from the power receiving circuit 50.In this way, the state of electromagnetic coupling between the powertransmitting apparatus 40 and the power receiving apparatus 60 can bechanged and information on this state is transmitted to the powertransmitting apparatus 40. In general, the switch is a switching devicesuch as a transistor or a MOSFET (metal-oxide semiconductor field-effecttransistor).

In the power receiving circuit 50 according to this embodiment, thepower receiving coil 51 and the capacitor 52 are connected to each otherin series to form an apparatus series resonant circuit. In addition, theC value and the L value are adjusted so that the apparatus seriesresonant circuit resonates at a resonance frequency. As described above,the C value is the capacitance of the capacitor 52 whereas the L valueis the inductance of the power receiving coil 51.

If the determination section 17B employed in the microcomputer 17 asshown in FIG. 4 determines that a metallic foreign substance existsbetween the power receiving apparatus 60 and the power transmittingapparatus 40 as evidenced by a result of a measurement which is carriedout by the detection circuit 10 of the power receiving apparatus 60 withthe configuration described above to measure the Q factor, the controlsection 17D employed in the microcomputer 17 executes control to stopthe transmission of electric power from the power transmitting apparatus40 to the power receiving apparatus 60. That is to say, the controlsection 17D employed in the microcomputer 17 controls an operationcarried out by the load adjusting section 55 to transmit a stop signal,which is used for stopping the transmission of electric power from thepower transmitting apparatus 40 to the power receiving apparatus 60,from the power receiving apparatus 60 to the power transmittingapparatus 40 by way of the power receiving coil 51. In accordance withthis stop signal received from the power receiving apparatus 60, acontrol section employed in the power transmitting apparatus 40 executescontrol to stop the sinusoidal-power generator 44. It is to be notedthat this control section itself is not shown in the figure.

As described above, the detection circuit 10 is employed in the powerreceiving apparatus 60. It is to be noted, however, that the detectioncircuit 10 can also be applied to the power transmitting apparatus 40.In either case, if the detection circuit 10 detects a metallic foreignsubstance existing between the power transmitting apparatus and thepower receiving apparatus, transmission of electric power from the powertransmitting apparatus to the power receiving apparatus is stopped.

4: Third Embodiment

In the case of the first and second embodiments, in order to compute theQ factor from a time-domain response waveform, the ADC 16 carries outsignal processing to find the envelop line of a voltage signal appearingon the reactance device of the resonant circuit. However, separatehardware serving as an envelop-line detecting circuit can be used tocarry out the transformation of the voltage signal appearing on thereactance device of the resonant circuit into the envelop line.

FIG. 11 is a diagram roughly showing a typical detection circuit 70according to a third embodiment of the present disclosure. In FIG. 11,an element having a function and a configuration which are essentiallyidentical with those of its counterpart shown in FIG. 3 is denoted bythe same reference numeral as the counterpart. In addition, detailedexplanation of each identical element is omitted.

The detection circuit 70 according to this embodiment is configured tohave the separate hardware serving as an envelop-line detecting circuitbetween the capacitor 12 of the detection circuit 10 shown in FIG. 3 andthe ADC 16. In FIG. 11, the envelop-line detecting circuit is shown as adashed-line block on the right side. The envelop-line detecting circuitincludes a diode 71, a capacitor 72 and a resistor 73. The diode 71 andthe capacitor 72 are connected to each other in series whereas theseries circuit consisting of the diode 71 and the capacitor 72 isconnected to the two terminals of the capacitor 12 in parallel. Inaddition, the resistor 73 is connected to the capacitor 72 in paralleland connected to the ADC 16 also in parallel.

If the detection of the envelop line is carried out by such separatehardware as is the case with the third embodiment, measurements andprocessing which are carried out at a later stage become very simple. Inthis case, it is no longer necessary for the ADC 16 to carry outprocessing to compute an envelop line from a voltage signal appearing onthe reactance device of the resonant circuit. That is to say, it isnecessary to merely measure voltages at two times.

5: Fourth Embodiment

If the detection of an envelop line is carried out by such hardware,measurements and processing which are carried out at a later stagebecome very simple. However, time-related information is still requiredby the microcomputer 17 for computation of the Q factor. For example,information such as the resonance frequency and amplitudes measured attwo measurement times is necessary. In this case, the amplitudes at twomeasurement times are amplitudes measured from the time-domain responsewaveform.

By the way, in order to find the resonance frequency by measurement, itis possible to adopt a technique for finding the resonance frequency bycomputing a vibration count representing the number of vibrations. Toput it concretely, the resonance frequency is typically found from thetime period of each of vibrations, the number of which is the vibrationcount defined as the number of vibrations in a prescribed time interval.This processing to find the resonance frequency is relatively simpleprocessing. However, it is necessary to separately provide a channel ora circuit or to prepare a channel detouring the envelop-line detectioncircuit described above as follows.

FIG. 12 is a diagram roughly showing a typical detection circuit 80according to a fourth embodiment of the present disclosure. In FIG. 12,an element having a function and a configuration which are essentiallyidentical with those of its counterpart shown in FIG. 11 is denoted bythe same reference numeral as the counterpart. In addition, detailedexplanation of each identical element is omitted.

In comparison with the detection circuit 70 shown in FIG. 11, thedetection circuit 80 shown in FIG. 12 has a limiter amplifier 81 and acounter 82.

A signal having a varying amplitude is supplied to the limiter amplifier81 from a node between the resonant circuit and the envelope-linedetecting circuit. The limiter amplifier 81 is a waveform formingsection for amplifying the input signal supplied thereto to a signalhaving a constant amplitude.

The counter 82 finds the vibration count of the constant-amplitudesignal received from the limiter amplifier 81 and supplies the vibrationcount to the ADC 16 and the microcomputer 17. Thus, the ADC 16 is notrequired to provide the microcomputer 17 with information such as thetime period of each of vibrations, the number of which is the vibrationcount defined as the number of vibrations in a prescribed time interval.

A computation formula is studied along with operations carried out bythe detection circuit 80 as follows. Equation 3 can be changed toEquation 14 from which Equation 15 is eventually derived. In Equation14, reference notation T denotes the time period of each of vibrations,the number of which is the vibration count. The vibration count is thenumber of vibrations in the time interval (t₂−t₁). The time period T isthe reciprocal of the resonance frequency f used in Equation 3. It is tobe noted that, in Equations 14 and 15, reference notation V₁ denotes avoltage appearing at the beginning of the time interval (t₂−t₁) whereasreference notation V₂ denotes a voltage appearing at the end of the timeinterval (t₂−t₁). The beginning of the time interval (t₂−t₁) is a timet₁ whereas the end of the time interval (t₂−t₁) is a time t₂.

$\begin{matrix}{Q = {{\pi \cdot \frac{1}{T} \cdot \frac{t_{2} - t_{1}}{1{n\left( \frac{V_{1}}{V_{2}} \right)}}} = {\pi \cdot \frac{1}{\frac{t_{2} - t_{1}}{{vibration} - {count}}} \cdot \frac{t_{2} - t_{1}}{1{n\left( \frac{V_{1}}{V_{2}} \right)}}}}} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack \\{Q = \frac{{\pi \cdot {vibration}} - {count}}{1{n\left( \frac{V_{1}}{V_{2}} \right)}}} & \left\lbrack {{Equation}\mspace{14mu} 15} \right\rbrack\end{matrix}$

As is obvious from Equation 15 serving as the computation formula, the Qfactor can be computed from the vibration count found by the computationformula. That is to say, it is not necessary to compute the time periodof a vibration. Thus, it is possible to further drastically reduce theload of the signal processing carried out by the ADC 16.

6: Fifth Embodiment

In a fifth embodiment, the Q factor is measured when the secondamplitude (second voltage) V₂ of the time-domain response waveform isstill within a predetermined range of amplitudes not including the firstamplitude (first voltage) V₁ of the time-domain response waveform.

The Q factor is found from Equation 15 by making use of the vibrationcount. Due to a quantization error generated by the ADC 16, however, thetime-domain response waveform may be attenuated excessively so that thesecond voltage V₂ undesirably has a magnitude close to 0. As a result,the Q factor cannot be computed correctly. This is because, even if theprescribed value of the vibration count changes, the voltage V₂ remainsat 0 (V₂=0) as it is.

In addition, if the time-domain response waveform is attenuated toolittle, that is, if V₁≈V₂, the quantization error generated by the ADC16 is also big. In order to solve these problems, the Q-factor measuringsection 17A employed in the microcomputer 17 measures the Q factor whenthe second amplitude representing the voltage V₂ of the time-domainresponse waveform is still within a predetermined range of amplitudesnot including the first amplitude representing the voltage V₁ of thetime-domain response waveform.

As an example, if the Q factor is computed when the voltage V₂ is stillin a range of about 40% to 25% of the voltage V₁, the error of the Qfactor is small in some cases. Thus, if precision is desired, theQ-factor measurement algorithm is set so that the Q factor is computedwhen the voltage V₂ becomes equal to a threshold value smaller than sucha range.

In accordance with the fifth embodiment, the quantization errorgenerated by the ADC 16 can be reduced so that the Q factor can be foundwith a high degree of accuracy. Thus, the precision of detection of ametallic foreign substance can be improved.

7: Sixth Embodiment

In addition, in the case of a high Q factor, it takes too much time forthe second amplitude of the time-domain response waveform to attain thethreshold value set in accordance with the fifth embodiment. In such acase, it is nice to measure the Q factor on the basis of a time limit orthe vibration count limit in place of such a threshold value. That is tosay, if the second voltage V₂ of the time-domain response waveform hadnot entered the predetermined range of amplitudes not including thefirst voltage V₁ of the time-domain response waveform within apredetermined time period, the second voltage V₂ is detected and the Qfactor is found at a point of time at which a time period determined inadvance lapses.

In accordance with the sixth embodiment, the time it takes to measurethe Q factor can be reduced to a limit not exceeding a time perioddetermined in advance.

8: Others

In the first to fifth embodiments, it is also possible to provide theresonant circuit with a single pulse or a standalone pulse in place of aplurality of pulses. In comparison with a single pulse, however, aplurality of pulses offer a merit that the signal level of thefrequency-domain response is high because much energy is supplied to theresonant circuit. Nevertheless, a single pulse also allows the Q factorto be measured.

In addition, in the first to fifth embodiments, the signal fetching timeof the ADC 16 may be long in comparison with the desired measurementtime. In such a case, two ADCs can be used to operate concurrently inorder to solve the problem caused by the long signal fetching time.

On top of that, in the first to fifth embodiments, pulses are suppliedto the resonant circuit employed in the detection circuit included inthe power transmitting or receiving apparatus from a signal sourceembedded in the detection circuit through a wire. However, the pulsescan also be supplied to the power transmitting or receiving apparatusfrom an external apparatus through magnetic coupling. Then, the powertransmitting or receiving apparatus makes use of the pulses to measurethe Q factor.

In the non-contact power transmission system shown in FIG. 10 forexample, pulses can be supplied from the power transmitting apparatus 40to the power receiving apparatus 60 through magnetic coupling. In thiscase, in accordance with the pulses, the power transmitting coil 42employed in the power transmitting apparatus 40 outputs a magnetic fluxto the Q-factor measurement coil 11 employed in the detection circuit 10of the power receiving apparatus 60 through the magnetic coupling and aresponse to the magnetic flux is read out to measure the Q factor.

The detection circuit 10 employed in the first to fifth embodiments canalso be applied to a non-contact power transmission system adopting anelectromagnetic resonance method or a non-contact power transmissionsystem adopting an electromagnetic induction method. In the followingdescription, the detection circuit 10 is also referred to as a detectionapparatus.

It is to be noted that the present disclosure can also be realized intothe following implementations:

(1) A detection apparatus including:

-   -   a resonant circuit provided with a Q-factor measurement coil and        one or more capacitors to serve as a circuit for receiving        pulses;    -   a response-waveform detecting section configured to detect the        waveform of a response output by the resonant circuit in        response to the pulses; and    -   a Q-factor measuring section configured to measure a Q factor of        the resonant circuit from the response waveform detected by the        response-waveform detecting section.

(2) The detection apparatus according to implementation (1), wherein theresponse waveform detected by the response-waveform detecting section isa time-domain response waveform.

(3) The detection apparatus according to implementation (2), wherein theQ-factor measuring section measures the Q factor of the resonant circuitfrom a first amplitude obtained from the time-domain response waveformat a first time and a second amplitude obtained from the time-domainresponse waveform at a second time lagging behind the first time by atime period determined in advance.

(4) The detection apparatus according to implementation (3), wherein,when the resonance frequency of the resonant circuit is denoted by f,the first amplitude obtained from the time-domain response waveform atthe first time t₁ is denoted by V₁, and the second amplitude obtainedfrom the time-domain response waveform at the second time t₂ is denotedby V₂, the Q-factor measuring section measures the Q factor inaccordance with the following equation:Q=πf·(t ₂ −t ₁)/1n(V ₁ /V ₂)

(5) The detection apparatus according to implementation (4), wherein theQ-factor measuring section measures the Q factor when the secondamplitude obtained from the time-domain response waveform is in apredetermined amplitude range not including the first amplitude.

(6) The detection apparatus according to implementation (4), wherein, ifthe second amplitude obtained from the time-domain response waveform hasnot entered a predetermined amplitude range not including the firstamplitude within a predetermined time period, the Q-factor measuringsection measures the Q factor by detecting the second amplitude at apoint of time after the lapse of the predetermined time period.

(7) The detection apparatus according to implementation (5) or (6),wherein the predetermined amplitude range set for the second amplitudeobtained from the time-domain response waveform is a range of 40% to 25%of the first amplitude obtained from the time-domain response waveform.

(8) The detection apparatus according to implementation (2), wherein,when the number of vibrations occurring within a predetermined timeperiod of the time-domain response waveform is denoted by“vibration-count,” an amplitude obtained at the start of thepredetermined time period is denoted by V₁, and an amplitude obtained atthe end of the predetermined time period is denoted by V₂, the Q-factormeasuring section measures the Q factor in accordance with the followingequation:Q=π·vibration-count/1n(V ₁ /V ₂)

(9) The detection apparatus according to any one of implementations (1)to (8), further including

-   -   a determination section configured to determine a state of        electromagnetic coupling between the Q-factor measurement coil        and an external apparatus by comparing the Q factor measured by        the Q-factor measuring section with a predetermined reference        value.

(10) The detection apparatus according to implementation (9), whereinthe state of electromagnetic coupling between the Q-factor measurementcoil and the external apparatus implies existence/non-existence of acircuit including any coil or a conductor between the Q-factormeasurement coil and the external apparatus.

(11) The detection apparatus according to implementation (1), whereinthe response waveform detected by the response-waveform detectingsection is a frequency-domain response waveform.

(12) The detection apparatus according to implementation (11), whereinthe Q-factor measuring section measures the Q factor from a bandwidthbetween two frequencies at each of which the amplitude of thefrequency-domain response waveform is 1/√2 times an amplitude at aresonance frequency of a series resonant circuit, the series resonantcircuit including one or more the capacitors and the Q-factormeasurement coil.

(13) The detection apparatus according to implementation (11), whereinthe Q-factor measuring section measures the Q factor from a bandwidthbetween two frequencies at each of which the amplitude of thefrequency-domain response waveform is √2 times an amplitude at aresonance frequency of a parallel resonant circuit, the parallelresonant circuit including one or more the capacitors and the Q-factormeasurement coil.

(14) The detection apparatus according to any one of implementations (1)to (13), wherein the pulses applied to the resonant circuit are a singlepulse.

(15) The detection apparatus according to any one of implementations (1)to (14), further including

-   -   a pulse generator configured to generate the pulses and apply        the pulses to the resonant circuit.

(16) The detection apparatus according to implementation (10), furtherincluding

-   -   a control section configured to execute control to stop output        of a power transmission signal from the external apparatus in        case it is determined that a circuit including any coil or a        conductor exists between the Q-factor measurement coil and the        external apparatus.

(17) A power receiving apparatus including:

-   -   a power receiving coil electromagnetically coupled to an        external apparatus;    -   a power receiving section configured to receive electric power        from the external apparatus through the power receiving coil;    -   a resonant circuit provided with a Q-factor measurement coil and        one or more capacitors to serve as a circuit for receiving        pulses;    -   a response-waveform detecting section configured to detect the        waveform of a response output by the resonant circuit in        response to the pulses; and    -   a Q-factor measuring section configured to measure a Q factor of        the resonant circuit from the response waveform detected by the        response-waveform detecting section.

(18) A power transmission system including:

-   -   a power transmitting apparatus configured to transmit electric        power by adoption of a non-contact transmission technique; and    -   a power receiving apparatus configured to receive the electric        power from the power transmitting apparatus,    -   wherein the power receiving apparatus includes        -   a power receiving coil electromagnetically coupled to a            power transmitting coil of the power transmitting apparatus,        -   a power receiving section configured to receive electric            power from the power transmitting apparatus through the            power receiving coil,        -   a resonant circuit provided with a Q-factor measurement coil            and one or more capacitors to serve as a circuit for            receiving pulses,        -   a response-waveform detecting section configured to detect            the waveform of a response output by the resonant circuit in            response to the pulses, and        -   a Q-factor measuring section configured to measure a Q            factor of the resonant circuit from the response waveform            detected by the response-waveform detecting section.

(19) A detection method including:

-   -   applying pulses to a resonant circuit provided with a Q-factor        measurement coil and one or more capacitors;    -   driving a response-waveform detecting section to detect the        waveform of a response output by the resonant circuit in        response to the pulses; and    -   driving a Q-factor measuring section to measure a Q factor of        the resonant circuit from the response waveform detected by the        response-waveform detecting section.

It is to be noted that the sequence of processes in the embodimentsdescribed above can be carried out by hardware or by execution ofsoftware. If the sequence of processes is carried out by execution ofsoftware, programs composing the software can be executed by a computerembedded in dedicated hardware or a computer in which the programs havebeen installed for the purpose of performing a variety of functions. Forexample, it is nice to make use of a general personal computer or thelike for executing programs installed therein as programs composingdesired software.

In addition, the apparatus and the system may be provided with arecording medium used for recording codes of the programs composing thesoftware to be executed to carry out functions of the embodiments. Ontop of that, it is needless to say that the functions can be carried outby the computer included in the apparatus or the system by reading outthe program codes from the recording medium. In place of the computer, acontrol apparatus such as a CPU may be used.

Typical examples of the recording medium used for recording the codes ofthe programs include a flexible disk, a hard disk, an optical disk, amagneto optical disk, a CD-ROM (compact disk read only memory), a CD-R(compact disk recordable), a magnetic tape, a nonvolatile card and aROM, to mention a few.

In addition, the computer executes the program codes read out from therecording medium in order to carry out the functions of the embodimentsdescribed above. On top of that, on the basis of instructions expressedby the program codes, typically, an OS operating on the computer carriesout part or all of actual processing. By carrying out the processing, itis also possible to implement the functions of the embodiments describedabove in some cases.

In addition, in this specification, steps of time-series processing canof course be carried out in a prescribed order along the time axis.However, the processing steps do not have to be carried out in aprescribed order along the time axis. That is to say, the processingsteps may also include processes to be carried out concurrently orindependently of each other, for example, steps of concurrent processingor steps of object-based processing.

Realizations of the present disclosure are by no means limited to theembodiments described so far and the implementations explained above.That is to say, the present disclosure can of course be implemented intoa variety of other typical modified versions and can of course beapplied to a variety of typical applications as long as the modifiedversions and the applications do not depart from the scope described inthe claims.

That is to say, the embodiments described above are no more thanpreferred typical implementations. Thus, a variety of technologicallydesired restrictions are imposed on the embodiments. However, thetechnological range of the present disclosure is by no means limited tothese embodiments unless otherwise particularly stated in anydescription that a restriction is imposed on the present disclosure. Forexample, each material mentioned in the description, the quantity of thematerial, the processing time, the processing order and the numericalcondition of each parameter are no more than preferred typical ones. Inaddition, dimensions in the figures referred to in the description, theshape of each of the figures and positional relations in each of thefigures are approximate ones.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2011-280059 filed in theJapan Patent Office on Dec. 21, 2011, the entire content of which ishereby incorporated by reference.

What is claimed is:
 1. An apparatus comprising: a resonant circuitincluding a coil and one or more capacitors; a signal source configuredto generate a signal that is input into the resonant circuit; a Q-factormeasuring section configured to (a) measure a first voltage at a firstterminal of the coil when the signal-source signal is input into theresonant circuit, and (b) obtain a Q-factor of the coil using themeasurement of the first voltage; and a determination section configuredto determine whether or not a foreign object exists in close vicinity ofthe coil by comparing the Q-factor obtained by the Q-factor measuringsection with a predetermined reference value.
 2. The apparatus of claim1, wherein the signal-source comprises: a pulse generator with circuitryto generate signal pulses; and a resistor to generate the signal basedon the signal pulses.
 3. The apparatus of claim 1, further comprising acontrol section operative to stop transmission of electric power by apower transmitter to a power receiver in response to detection of aforeign object in the close vicinity of the coil.
 4. The apparatus ofclaim 1, wherein the frequency of the signal is equal to a resonancefrequency of the resonant circuit.
 5. The power transmitting apparatusof claim 4, wherein the frequency of the signal is equal to a resonancefrequency of the resonant circuit.
 6. The power transmitting apparatusof claim 4 configured to obtain the Q-factor of the coil before powertransmission occurs.
 7. The power transmitting apparatus of claim 4,configured to determine the existence of a foreign object in the closevicinity of the coil when the Q-factor obtained by the Q-factormeasuring section is lower than the predetermined reference value. 8.The apparatus of claim 1, wherein the Q-factor measuring section isconfigured to measure the first voltage twice, and obtain the Q-factorusing the two measurements of the first voltage.
 9. The apparatus ofclaim 8, wherein the Q-factor measuring section is configured to measurethe first voltage at a first time and at a second time lagging behindthe first time by a predetermined time period.
 10. The apparatus ofclaim 8, wherein the Q-factor measuring section is configured to obtainthe Q-factor using Equation 3:$Q = {\pi\;{f \cdot \frac{t_{2} - t_{1}}{1{n\left( \frac{V_{1}}{V_{2}} \right)}}}}$where, f is a resonance frequency of the resonant circuit, V1 is thefirst measurement of the first voltage at a point in time t1, and V2 isthe second measurement of the first voltage a point in time t2.
 11. Theapparatus of claim 8, wherein the Q-factor measuring section isconfigured to measure the first voltage at a second time when the firstvoltage is in a predetermined range including the first voltage at afirst time.
 12. The apparatus of claim 11, wherein the predeterminedrange set for the first voltage at the second time is a range of 40% to25% of the first voltage at the first time.
 13. The apparatus of claim8, wherein, the Q-factor measuring section is configured to measure thefirst voltage again at a second point of time after the lapse of adetermined time period as when the first voltage has not entered apredetermined range not including the first voltage at a first point intime within the predetermined time period.
 14. The apparatus of claim13, wherein the predetermined range set for the first voltage at thesecond point in time is only in a range of 40% to 25% of the firstvoltage at the first point in time.
 15. The apparatus of claim 8,wherein the Q-factor measuring section is configured to obtain theQ-factor using Equation 15:$Q = \frac{{\pi \cdot {vibration}} - {count}}{1{n\left( \frac{V_{1}}{V_{2}} \right)}}$where, V1 is the first measurement of the first voltage at a point intime t1, V2 is the second measurement of the first voltage a point intime t2, and vibration-count is a count of vibrations in aconstant-amplitude signal related to the first voltage.
 16. Theapparatus of claim 1, wherein the Q-factor measuring section isconfigured to measure a second voltage at a second terminal of the coilwhen the signal-source signal is input into the resonant circuit, andobtain the Q-factor using the measurements of the measurements of thefirst voltage and the second voltage.
 17. A power transmitting apparatuscomprising: a resonant circuit including a coil and one or morecapacitors; a signal-source configured to input a signal to the resonantcircuit; a Q-factor measuring section configured to measure a firstvoltage at a first terminal of the coil and a second voltage at a secondterminal of the coil when the signal-source signal is input into theresonant circuit, and to obtain a Q-factor of the coil using the firstvoltage and the second voltage; a determination section configured todetermine whether or not a foreign object exists in close vicinity ofthe coil by comparing the Q-factor obtained by the Q-factor measuringsection with a predetermined reference value; and a power transmittingsection configured to transmit electric power wirelessly to a powerreceiving apparatus.
 18. The power transmitting apparatus of claim 17,wherein the signal-source comprises: a pulse generator with circuitry togenerate signal pulses; and a resistor to generate the signal based onthe signal pulses.
 19. The power transmitting apparatus of claim 17,further comprising a control section operative to stop transmission ofelectric power by the power transmitter to the power receiver inresponse to detection of a foreign object in the close vicinity of thecoil.
 20. A method comprising: providing a resonant circuit including(a) a coil and one or more capacitors, (b) a signal-source configured togenerate a signal that is input into the resonant circuit, (c) aQ-factor measuring section configured to (1) measure a first voltage ata first terminal of the coil when the signal-source signal is input intothe resonant circuit, and (2) obtain a Q-factor of the coil using themeasurement of the first voltage, and (c) a determination sectionconfigured to determine whether or not a foreign object exists in closevicinity of the coil by comparing the Q-factor obtained by the Q-factormeasuring section with a predetermined reference value; inputting thesignal-source signal into the resonant circuit; measuring the firstvoltage at the first terminal; obtaining a Q-factor of the coil usingthe measurement of the first voltage; and determining whether or not aforeign object exists in close vicinity of the coil by comparing theQ-factor obtained by the Q-factor measuring section with a predeterminedreference value.
 21. A power transmitting apparatus comprising:providing a resonant circuit including (a) a coil and one or morecapacitors, (b) a signal-source configured to input a signal to theresonant circuit, (c) a Q-factor measuring section configured to measurea first voltage at a first terminal of the coil and measure a secondvoltage at a second terminal of the coil when the signal-source signalis input into the resonant circuit, and to obtain a Q-factor of the coilusing the first voltage and the second voltage, (d) a determinationsection configured to determine whether or not a foreign object existsin close vicinity of the coil by comparing the Q-factor obtained by theQ-factor measuring section with a predetermined reference value, and (e)a power transmitting section configured to transmit electric powerwirelessly to a power receiving apparatus; inputting the signal-sourcesignal into the resonant circuit; measuring the first voltage at thefirst terminal; measuring the second voltage at the second terminal;obtaining a Q-factor of the coil using the measurement of the firstvoltage and the measurement of the second voltage; and determiningwhether or not a foreign object exists in close vicinity of the coil bycomparing the Q-factor obtained by the Q-factor measuring section with apredetermined reference value.